The humoral mechanism of essential, benign, renal hypertension and of acute neurogenic hypertension continues to represent the principal object of our studies. 1. The concentration of renin in systemic blood of dogs will be investigated under various experimental conditions in which the presence of renal ischemia is the pathogenetic factor responsible for the alteration of the vasopressor humoral mechanism. 2. Antirenin produced by the immunization of animal and man can be applied as a specific inhibitor of renin, to evaluate the participation of renin in the maintenance of high blood pressure under various experimental and clinical conditions. 3. Microassay procedures are now available which permit a study of the biochemical (immunochemical or enzymatic) mechanism of the renin-antirenin reaction at physiological levels of renin concentration. 4. The storage of antirenin in various tissues will be investigated as well as its release into the blood by various agents and mechanisms (adrenal cortical steroids, ACTH, anaphylaxis, hypotensive drugs). 5. Attempts at further purification of human renin will be undertaken, by affinity chromatography from a column of sepharose gel, coupled with a potent competitive inhibitor of renin, such as pepstatin or the d-leucine 6-octapeptide, representing a segment of renin substrate.